In various multistage turbomachines used for energy conversion, such as gas turbines, a fluid is used to produce rotational motion. Referring to FIG. 1, an axial flow gas turbine 10 includes a multi-stage compressor section 12, a combustion section 14, a multi stage turbine section 16 and an exhaust system 18 arranged along a center axis 20. Air at atmospheric pressure is drawn into the compressor section 12 generally in the direction of the flow arrows F along the axial length of the turbine 10. The intake air is progressively compressed in the compressor section 12 by rows of rotating compressor blades, thereby increasing pressure, and directed by mating compressor vanes to the combustion section 14, where it is mixed with fuel, such as natural gas, and ignited to create a combustion gas. The combustion gas, which is under greater pressure, temperature and velocity than the original intake air, is directed to the turbine section 16. The turbine section 16 includes a plurality of airfoil shaped turbine blades 22 arranged in a plurality of rows R1, R2, etc. on a shaft 24 that rotates about the axis 20. The combustion gas expands through the turbine section 16 where it is directed in a combustion flow direction F across the rows of blades 22 by associated rows of stationary vanes 24. A row of blades 22 and associated row of vanes 24 form a stage. In particular, the turbine section 16 may include four stages. As the combustion gas passes through the turbine section 16, the combustion gas causes the blades 22 and thus the shaft 24 to rotate about the axis 20, thereby extracting energy from the flow to produce mechanical work.
Nondestructive examination (hereinafter “NDE”) techniques, such as ultrasonic testing techniques, have been used to evaluate the manufacturing quality and operational integrity of turbine structures and components. In one type of ultrasonic testing technique known as immersion testing, a turbine structure or component to be tested (i.e. test object) is immersed in a tank of water. An ultrasonic transducer is also placed in the water and spaced apart from the test object to form a column of water between the water and the test object that facilitates the transmission of ultrasonic energy generated by the ultrasonic transducer to the test object. The ultrasonic transducer then generates ultrasonic energy that is transmitted through the water toward the test object. Ultrasonic energy is reflected from the test object and is detected in order to determine whether flaws or defects are present in the test object.
It is desirable to perform ultrasonic testing of turbine structures or components of turbines that are currently operational, i.e. turbines that are in the field. However, the turbine structure or component must be removed from the turbine and then transported to an NDE laboratory for inspection in order to perform immersion testing, which undesirably delays the inspection process.